(a) Field of the Invention
The present invention relates to an apparatus and a method of converting image signal for four-color display device, and a display device including the same.
(b) Description of Related Art
In recent, flat panel displays have been developed widely such as organic light emitting displays (OLEDs), plasma display panels (“PDPs”) and liquid crystal displays (“LCDs”) instead of heavy and large cathode ray tubes (“CRTs”).
The PDPs are devices which display characters or images using plasma generated by gas-discharge, and the OLEDs are devices which display characters or images using electric field light-emitting of specific organics or high molecules. The LCDs are devices which display desired images by applying electric field to liquid crystal layer between two panels and regulate the strength of the electric field to adjust the transmittance of light passing through the liquid crystal layer.
Although the flat panel displays usually display colors using three primary colors such as red, green and blue, recently, especially in case of LCDs, for increasing the luminance, a white pixel (or a transparent pixel) is added to the three-color pixels, which is called four-color flat panel displays. The four-color flat panel displays display images after converting inputted three-color image signals are into four-color image signals.
Generally, the lower is chroma, the larger is the gamut of the luminance (or brightness) which even the same color can have, and alternatively, the higher is chroma, the more limited is the gamut thereof. Therefore, in the four-color flat panel displays, an effect of the luminance increase due to addition of the white pixel depends on the chroma. With this, a problem of color-change or simultaneous contrast occurs. The simultaneous contrast means that, for example, when watching smaller squares of the same color located within two or three larger squares, the smaller squares of the same color are recognized differently depending on the luminance of the larger squares.